Common CodeIgniter Errors Every Developer Faces (and How to Fix Them)

Meta Description: Fix the most common CodeIgniter errors like 404 routes, database connection issues, CSRF token mismatch, and autoloading failures. Learn solutions that save time during development.

🚀 Introduction

Whether you're a beginner or an experienced PHP developer, CodeIgniter (especially CodeIgniter 4) can sometimes throw frustrating errors during development. The good news? Most of them are common, and there are proven fixes.

Here’s a list of the most frequent CodeIgniter errors and how to solve them quickly.

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❌ 1. 404 Not Found - Controller Not Loading

Error: You hit a route like /user/profile but get a 404 page.

Causes & Fix:

• The method in your controller is not public.
• Check the controller filename and class name match exactly (case-sensitive).
• Verify the route exists in app/Config/Routes.php.
• Default route might be missing: $routes->get('/', 'Home::index');

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⚙️ 2. Database Connection Error

Error: "Unable to connect to the database" or "Access denied for user".

Solution:

• Check your database credentials in .env or app/Config/Database.php.
• Use hostname = localhost (not 127.0.0.1 if MySQL is socket-based).
• Ensure MySQL is running and listening on the expected port.

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🛡 3. CSRF Token Mismatch Error

Error: Submitting a form gives “The action you requested is not allowed.”

Fix:

• Ensure is added inside your form.
• CSRF protection is enabled in app/Config/Filters.php.
• If using AJAX, send the token with your request headers or body.

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📦 4. Class Not Found or File Not Loading

Error: "Class not found: App\Controllers\MyController"

Cause & Fix:

• Check if namespaces are correctly defined: namespace App\Controllers;
• Composer autoload might be outdated — run: composer dump-autoload
• Check the file naming: MyController.php must match the class name.

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🧾 5. Autoload Not Working

Problem: You added a library/helper/model but it's not recognized.

Fix:

• Ensure it's autoloaded in app/Config/Autoload.php.
• Or load manually in the controller: $this->load->helper('url'); (CI3)
• For CI4, use: helper(['url', 'form']); at the top of the method or controller.

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⛔ 6. ErrorException: Trying to access array offset on null

Cause: You’re accessing an array index from a variable that’s null or not an array.

Fix:

• Use isset() or null coalescing operator ?? to check before accessing.
• Example: $data['title'] = $input['title'] ?? 'Default Title';

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🛠 7. Session Not Working or Not Saving

Issue: Flashdata or session values are not persisting.

Solution:

• Ensure 'sessionDriver' => 'CodeIgniter\Session\Handlers\FileHandler' is correct in Config\App.php.
• Writable directory permissions must be correct (especially app/writable/session).
• Use $session->set() and $session->get() properly.

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✅ Conclusion

Every framework has its quirks, and CodeIgniter is no exception. However, these common issues are usually easy to fix once you know what to look for.

Tip: Bookmark this post so you don’t waste time next time you hit one of these errors!

Happy Coding 🚀

📎 Tags:

CodeIgniter, CodeIgniter 4, PHP Errors, Troubleshooting, CI4 Routing, Laravel vs CodeIgniter, Web Development